Method of catalyst control in organic reactions



March 25, 1952 T. B. HuDsoN METHOD -OF cATALYsT CONTROL 1N4 ORGANIC REACTIONS Filedoct. 14, 1947 3 Sheets-Sheet l `SOLVENT 6| March 25,1952 T. B. HUDSON 2,590,539

i METHQD- oF CATALYST CONTROL IN ORGANIC REACTIONS Filed ocx. 14, 1947 :s sheets-'sheet 2 BF3 AND PROPANE MAKE UP 53 BF3 AND PRoPANE BFa REFRIGERA-r 7 BFS PROPANE BE, a soLvENT RECOVERY PROCESSES BUTENES soLvENT lREACTION CHAMBER INVENTOR THOMAS B. HUDSON BY i 'L ATroRNEYs March 25, 1952 1. B. HUDSON 2,590,539

METHOD OF CATALYST CONTROL IN ORGANIC REACTIONS Filed oct. 14, 1947 s sheets-Sheet s US ED CATALYST REACTION PRODUCTS REGENERATED cATALYsT REACTI CHAMBE EXOTHERM IC REACTANTS CATALYST CONVEYOR INVENTOR. THOMAS B. HUDSON ATTORNEYS Patented Mar. 25, 1952 METHOD F CATALYST CONTROL IN ORGANIC REACTIONS Thomas B. Hudson, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application October 14, its?, Serial No. 779,786

y iciaims. (creto-449.6)

This invention relates to improvements in catalytic processes. More particularly it relates vto novel methods of bringing mobile catalysts into contact with reactants. It has particular relevance to organic reactions such as hydrocarbon conversions. This application is a continuation-impart of my copending application Serial No. 453,265, filed August 1, 1942, now U. S. Patent 2,429,161, issued October 14, 1947.

The use of catalysts has come to be of primary importance in industry. Catalysts may greatly accelerate the rate of reaction for many processes so that either a much more rapid conversion at a given temperature is obtained, or a much lower temperature may be used toaccomplish a given conversion. In fact in many cases, catalysts of one kind or another have made possible the carrying out of reactions which previously had been believed impossible. While catalytic action cannot cause a reactionto occur which is thermodynamically impossible, it may be the only means of attaining a practical Lrate of reaction for a given conversion. Utilization of elevated 4temperatures frequently cannot be relied on due 'to 4shifts in equilibrium concentrations or due to the'occurrence of undesired side reactions. Many reactions will not take place atpracticable tem- I volved, the search for eiective catalytic materials has commanded the attention oi a great segment of the technical world. Since the turn of the century, the successful results of these investigations have given rise to numerous new industries,

, as well as providing greatly improved methods for the older industries.

The petroleum industry may be taken as one outstanding example. Whereas fteen to twenty- `ve years ago non-catalytic processes were utilized almost exclusively in all fields of petroleum rening, the trend now is toward catalytic processes, ywhich are rapidly replacing older methods with results which are more satisfactory not only in increased efficiency but also in producing entirely new products.

Present day needs call for high-octane gasoline, and various other fuels having special requirements. Aviation fuels in particular must now be prepared by blending al- 2 most pure individual hydrocarbons or hydrocarbon types in order to meet the demand for fuels which will readily respond to specific operating conditions. Offshoots from the petroleum industry, such as the production of synthetic rubbers, call for preparing very pure single hydrocarbons for use as raw materials.

Not only.4 is the chemical composition of the catalytic material of importance in attaining specio results in chemical conversions, but its physical form, activation treatments, impurities, methods of contacting with reactants, reactivation processes, etc., all exert their influences on the course of the conversions beingcatalyzed. The particular products and yields thereof obtained are also dependent to a great extent'on such reaction conditions as pressure, temperature, time of contact between reactants and catalyst, etc.. Careful control of all these variables is required for production of the optimum quantities and quality oi products. Organicconver- .lsions are particularly susceptible to the eects of these various factors, due to the numerous sifde reactions which can occur.

One of the most important influences in 4the course of catalyzed reactions, and frequentlyA one of the most difcult to control, is temperature. Most of such reactions are either highlyendothermic or highly exothermic, and maintenance of the desired range of temperature is a major operating diiiiculty. The activity of a catalyst for a denite conversion-is usually of economic signicance only within a fairly narrow temperature range, and a particular process using that catalyst must obviously be operated within the active range. This condition is shown by the great change in the degree of conversion usually occurring with relatively small temperature changes. r

Thus, in the case of endothermic reactions, the temperature drop which normally occurs may be so pronounced that the rate of conversion will rapidly decrease to an unecomonic level. In the case of exothermic reactions, a rise in temperature normally occurs which, if not controlled in some way, will rapidly .bring the temperature to a point Vat which undesirable side reactions occur. In fact, such side reactions may frequently become the predominant reaction at temperatures only relatively slightly above those required for the desired conversions. Or, the principal reaction rnay be caused to proceed too rapidly, in which case the reaction rate and temperature become uncontrollable with undesirable or even diso i temperature within narrow limits throughout avreaction zone for either endothermic or exotliermic reactions is not only highly desirable but is ordinarily a necessity.

' Many methods have been offered for the control of temperatures in catalytic conversions, usually involving complicated apparatus designs whereby indirect heat transfer is utilized in connection with portions of catalytic materials so small as to allow sufficient heat to pass from or into the catalyst mass to accomplish the desired results. For example, particles of solid catalyst have been packed into relatively small .tubes so that no portion of the catalyst is more than say one inch from a tube wall, and a number of such tubes connected in parallel, with a heat transfer medium being circulated about the exterior of the tubes. An alternative method has been to provide a system of coils or the like within a catalyst mass so that a heating or cooling medium, as required, may be circulated throughout the catalyst bed. Similar arrangements have been provided for reaction vessels employing moving catalysts. However, these methods have not been able to compensate fully for the low thermal conductivity of the -usual catalysts. Furthermore, the surface of the tubes or other elements through which the heat transfer takes place. is at a temperature appreciably different from that generally prevailing in the reaction zone. This is disadvantageous, particularly with endothermic reactions where, in the case of hydrocarbon conversions for example, cracking, coke formation and other reactions takev place on the superheated surfaces, which causes loss of o materials and fouling of equipment.

Other methods proposed for compensating for heat of reaction include superheating of reactants involved in endothermic processes above optimumternperatures, or the converse, that is Vinsuiii'cient preliminary heating of exothermic reactants. The inefficiencies of such methods are obvious. Catalyst poisoning may sometimes occur to an increased extent at either lowered or in'creasedtemperature.

Probably the most common method of'bringing solid catalysts into contact with reactants is to place the catalyst in a reaction chamber, and pass the reactants therethrough at the desired flow'rate, temperature, and pressure. However, in many cases, it has been found useful to cause the solid catalyst particles to move through the reaction zone. Also in the case or" gaseous or liquid catalysts, the catalyst is frequently passed through the reaction zone. Such catalysts, whether solid, liquid, or gaseous, which are passed through a reaction zone, are referred to herein as mobile or iiuent catalysts. They may be passed either concurrently with or countercurrently to the reactants, depending upon the reactions beingcatalyzed, the catalyst, and other variables.

Itis an object of this invention to provide novel catalytic processes. Another object is to provide improved methods of operating catalytic systems, particularly those employing mobile catalysts. Another object is to enable a more delicate control of catalyzed organic reactions, particularly hydrocarbon conversion. A further object is to provide improved methods of contacting mobile catalysts with reactants. A further object is to provide for the control of catalyzed reactions with respect to temperature and/or products obtained. Yet another object is to permit' controlled variation in the quantity and/or activity of catalyst present at all points in a reaction zone. A still further object is to provide for the introduction of one or more catalysts into a reaction zone at a plurality of points. Another object is to provide for the concurrent or countercurrent Iiow of catalyst thus introduced relative to the flow of reactants. Another object is to correlate the introduction of catalyst with certain reaction conditions in an exact manner so as to compensate, at least in part, for change in temperature and/ or change in concentration of reactants or other reaction conditions. A further object is to provide for reactivating catalysts which have become deactivated in which processes so that the reactivated catalyst may be reintroduced into contact with reactants. Still another object is to effect an exothermic reaction under conditions of increasing temperature gradient in the direction of flow of reactants 'while regulating the catalyst content of the rethe catalyst action mixture as a function of the temperature. A further object is to er'e'ct the polymerization of unsaturated compounds. Yet another object is to apply the principles of the invention as disclosed herein to the reaction of hydrogen with carbon oxides, particularly carbon monoxide, to form orga-nic compounds including hydrocarbons and oxygenated derivatives thereof.l Other objects and advantages of the invention will become apparent from the following disclosure.

My invention is essentially a method for carefully controlling. catalytic processes by the multipoint addition of catalyst, specifically corre-- lated'with reaction conditions. Specific methods of operating are disclosed which are especially adapted for given types of conversions. These different methods, while each employing the introduction of vcatalyst into a reaction zone at a plurality of points, are not at all to be considered as exact equivalents inasmuch as each is particularly designed to give optimum results for the given application, as will be more `ully explained. Iam aware that catalytic-materials have occasionally in the past been described as being introduced into a reaction zone at more than one point. Such disclosures, however, have been vague, indefinite, and most unenlightening as to the purposes involved and exact results accomplished. I have found specic relationships between catalysts introduction and reaction conditions, and have devised novel methods of correlating the various factors involved whereby new and highly useful results arc accomplished, as will be apparent from the detailed teachings hereinbelow set fort From one point of view, the invention may be considered as comprising three principal operational modifications. A first modification has to do with catalysts which are miscible with one or more reactants, either by 'virtue of mutual solubility or because of small particle size of the catalyst allowing its suspension in reactants. Such a suspension may be in a more or less stable form, or in a relatively separable form in which is maintained in suspension by means or" turbulent flow, static charges, etc. Finely divided solid catalysts are frequently suspended in gaseous reactants and passed through a zone maintained under desired reaction conditions. Such catalysts have been called fluid catalysts, which is in actuality a misnomer. Howevery they vdo often pass at the same rate of now as the reactants and the entire mixture may be handled more or less as a single Afluid. As is well known in the art, the term uid when applied to'powdered solid catalysts includes the suspensionif'same in reactants under conditions of straight-through flow, hindered settling or even in fluifd'zfed beds. Accordingly, I may define "iiuid catalysts broadly to include not only gascous andliquid catalysts, but also finely divided solids suspended in reactants. A second modification 'involves catalysts which are immiscible with reactants undergoing treatment, with the catalyst'l passing concurrently with the reactants through Y,the reaction zone, generally at a rate different than the rate of ow of reactants. A third modification relates to catalytic materials which are non-miscible with reactants wherein the catalyst after being introduced at a plurality of points 'subsequently moves countercurrent to the' reactants. In some cases there is a combina-tion of the modifications, in `yhich at least one reactant passes countercurrently to at least one other reactant, in which case the catalyst will `move `concurrently with one reactant and countcrcurrently to another reactant.

The choice of operating methodx and the manner ofvu applying that method, will of course be based ori the type of catalyst, reaction and other `factors. l However, the choice of points for inscribed.

By the vuse of my invention'l may so inter-relate the various factors such as temperature; flow rate of reactants, diluentsy and catalyst-catalyst -Vactivity; time of contact between reactants and catalyst; etc;; as to provide a most complete and delicate control over the nature and extent of relaction at'all points in the reaction zone.

As pointed out above, temperature control is posslbly the maior problemin carrying out exotherrnic and cndotherinic reactions. The presont; invention provides methods for maintaining proper reaction velocity vin the face of increasing or decreasing temperatures, or of avoiding such increases-or decreases in temperature.

In the-case oi` endothermic reaction, the cata- .lyst may be introduced at a plurality of pointsb spa-ccd in 4the direction of flow of reactants for concurrent-dow therewith.' The amount of catalyst issinallest in the first portion of the reaction 'zonej-a'nd largest in the last portion of the zone,

'dothcrni'al reaction takes up heat. The amount of catalyst` added at each point is chosen so as to provid ruiiicient additional catalytic activity to maintv ngthe rate of reaction in spite of the lowered emperature existing at that point. Thus, eveiy'tvoughunder ordinary conditions the rate of reaction at a temperature, say or 100 F., lower rthan the optimum reaction temperature would-be several times less, resulting in `much lowered. conversion in the latter portions of the reaction none, the additional catalyst compensates at least partially for the lowered temperature and may maintain substantially constant conversion throughout the zone if added in sufllcient,V quantity at each point.

Another manner of utilizing this invention for endothermic reactions involves multipoint addition of ycatalyst with subsequent countercurrent flow relative to the reactants. This may be done 6 especially if the catalyst used undergoes veryvrapid deactivation at the" given reaction conditions. In this case, the rate of introduction and flow of catalyst is regulated so that it is substantially spent, that is, deactivated for the reaction, by the time it exits from the reaction zone. yThe point of exit of catalyst is at or near the point of entrance of reactants.- Accordingly, the reactants first contact a relatively large mass of substantially deactivated catalyst containing only a small proportion of active catalyst introduced at the later (earlier, with respect to reactants) points of the reaction Zone. The total activity is quite limited, and smaller here than at subsequent points. As the reactants pass on through the zone, they Contact smaller quantitiesrof total catalyst, but the catalyst contacted has` greater activity. The deactivated catalyst also has a `diluent effect, and a unit volume of reactants passes through the first portions of the reaction zone more rapidly than it does though the last portions.' Flow of reactants continues countercurrent to the flow of catalyst until just before leaving the reaction zone they come in contact with a relatively small quantity of catalyst having very high activity. The increasing. catalyst activity `thus encountered by the reactants as they flow enable the reaction rate to be maintained in spite of the Vdecreasing temperature caused by the endothermic nature of the reaction. The increments of catalyst added at the points of lowest temperature may, if necessary, be larger than those added at the points of higher temperatures, the quantity added,- rate of addition and rate of now through the reaction zone always being so chosen and related as to compensate at least inV part for the variation-of reaction rate with temperature. Alternatively or additionally catalyst regenerated at a high temperature may bel used in such quantities as to maintain reaction temperature constant-or to minimize the extentjof temperature drop.

An exothermic reaction may be handled inv-a somewhat diierent manner, but with the same end in view, namely, thecontrol of catalyst activity and contact time between catalyst and'reactants so as to compensate, in part at least, for variation of rate of reaction with temperature. Generally, the most satisfactory control is obtained by use of -countercurrent flow of reactants and catalyst introducedg multipoint. Reactants first are contacted withfa relatively large volume of catalyst, the ratio of'catalyst activity to volume of reactants being greatest at this point and progressively decreasing inthe direction of reactant ow, while the temperature correspondingly in creases. At the higher temperature levels,jless catalyst activity is encountered, so that reaction velocity may be maintained as nearly constant as desired. Near the exit from the reaction zone, the reactants are contacted'with the smallest quantity of catalyst, this quantity, however, being suhicient to maintain the desired rate of reaction. The advantages of operating in this manner may readily be seen by contrasting with prior methods wherein either the heat of reaction must be removed by diilicult means heretofore discussed, or, if the temperature is allowed to increase, contact with equal increments'of catalystcombined with the higher temperatures causes greatly increased reaction rates.

Another method ofcontrolling exothermic reactions which is particularly, although not exclusively adapted forfuse with catalysts which become rapidly deactivated, is the concurrent ilow 7 circuiti-point-introduccd catalyst. I nsuch usage, a iirst portion of catalyst is introduced either along with the reactant feed or separately into the reaction zone near the point of entrance of the reactants, and the next portion of catalyst, generally smaller, is added at a point at which the iirstportion is mostly deactivated; atany-rate, the relationship of the amount of catalyst thus introduced to the extent of deactivation of previously introduced catalyst is such that the ratio of total catalyst activity to volume of reactants at that point is less than at the earlier point of catalyst introduction, the diiierence being generally inversely'proportional to temperature. It would not be at all desirable to introduce catalyst increments of equal activity at equal points while the temperature is rising. As-the ternperaturc increases in the direction of flow of react-ants, the catalyst activity decreases so as to :avoid e. constantly increasing conversion rate as would normally he encountered.

The above discussion is directed towards proccsses carried out under adiabatic, or at least partially adiabatic conditions in which the heat of reaction causes a temperature gradientto exist A along the direction oi flow of reactants. A combination oi indirect heat exchange to partially overcome heat oi reaction, vwith the controlled introduction of catalyst as described above, may be used for exotherrnic or endothermic reactions.

In case it is desired to maintain substantially isothermal conditions in endothermic or exotherniic reactions by means o1" indirect heat exchange or other methods, this'invention may be utilized to obtain a more satisfactory control oi reaction and to simplify the temperature control. When reactants are passed through a stationary bed oi catalyst, or contacted with a single portion of mobile catalyst, there tendency forthe reaction to proceed too rapidly at first, with consequent overheating or cooling, as the case may be, at the first point of Contact between react-ants and catalyst and too rapid catalyst deactivation :it that point. However, by adding catalyst to the reaction zone in controlled increments in l accordance rwith my invention, the extent ci reaction and temperature may he maintained under strict control since reactants are contacted with a limited portion of catalyst, and are not contacted with an additional portion until the temperature is 'drought back to the desired value. Tie catalyst is not added haphazardly, but the addition is careuly correlated with the amount ci heat produced or consumed by the .reaction ndvfith the amount removed or introduced, so as to'avoid localized Vspots oi overheating or excessive cooling. l

Catalyst and reactants may flow `countercurrently or concurrently. depending upon the type of reaction, catalyst. etc.. the proper modications being readily chosen in view-ofthe detailed disclosures offered `herein.

Other operating: problems frequently encountered in catalyticreection-s involve'catalyst deactivo tion and inf-e .s for avoiding saine-offer reacng catalyst, the activity of which has dropped to'an uneoonomic level. Mobile catalysts a e generally subjected to reactivation treatment o .her after each passage through a reaction zone, or a portion only may be treated each time to keep the overall activity at the desired level. One of the advantages of mobile catalysts over stationary catalysts is that control of regeneration is thu-s obtained in a fairly simple manner. However, only thek overall activity is thus affected, the

actuaLactivity at any particular pointin the reactionzonebeing dependent upon conditions therein which are not readily changed with respect. to deactivation of catalyst which is occurring.r For example, many catalysts will be subjected toa rather extensive deactivation in a relatively small first portion of the reaction zone, due to temperature conditions, poisons, etc., with deactivation in subsequent portions of the reaction zone continuing at a much slower rate. in such a case, it will be seen that while the average or overall. ac.- tivity may be regulated, the uneven loss in activity causes an ineiilcient operation.

My invention provides a means for controlling the activity of mobile catalysts at any point in a reaction zone. This may readily be accomplished by controlling the quantity and/or activity of catalyst introduced at the different points. Thus in certain cases, partially or completely deactivated catalyst may be admixed in varying proportions With fresh or reactivated catalyst to give the desired activity for introduction at any particular point. In fact, in some cases more than one different type of catalyst may be used for introduction at diierent points into a single reaction zone to give controlled activity, which may be either maintained constant or varied from point to point to meet the needs of the particularv reaction being catalyzed. Examples given herein will serve to point out more clearly a few of, the many ways in which controlled variation or constant activity of catalyst is obtained and correlated with other reaction conditions through use of this invention.

Another method by which my invention makes possible a more eiective use of catalyst is by controlling the quantity and/or activity of mobile catalyst in a reaction zone in relation to the concentration of reactants existing at various points in the zone. The change in concentration of reactants in a reaction zone depends uponv theextent of conversion occurring. Ii, as in many cases a substantially complete conversion of reactants to products is desired by the time the-reaction mixture leaves the reaction zone, it will be seen that the concentration of at least one reactant must approach zero at the reaction zone exit.

In many other reactions, however, an equilibrium may exist which prevents, or economic considera'- tions may make undesirable, a complete conversion. The extent of conversion may vary greatly with the type of reaction being catalyzed, one process involving say a one per cent conversion per pass while another may accomplish forty. sixty, or more per cent conversion in one pass. Ordinarilyn case the percentage conversion is low, the loss in concentration of reactants as the reaction proceeds does not great-ly affect the reaction'rate. However, in the case of higher conversions ranging on up to 100 per cent, the lowered concentrations of reactants existing in the latter parts of the reaction zone may greatly decrease the reaction rate, even though expediente such as using a large excess of one reactant or the like are resorted to. By controlling the multipoint introduction of catalyst in accordance with the decrease in reactant concentration, I may partially or completely compensate therefor, and avoid too great or any decrease in reaction rate by providing more catalyst activity at the points of lower concentration. The dilution effect of the catalyst is also to be considered. Again, the catalyst may pass either concurrently or countercurrently to the reactant depending upon the various factors involved for any particular reaction.

It is to be understood that the various methods of utilizing the present invention, that is, for example, by controlling the introduction of catalyst to compensate for changes in temperature, catalyst activity, reactant concentration, etc., may be used either alone or in various combinations, one with the other, as will be well understood by one skilled in the art in view of the full and complete disclosure given herein. Obviously the choice of one or a combination of methods of operating will have to be made with dueconsiderationfor the reactions being catalyzed, the type of catalyst most suitable, the extent of reaction, the thermal changes involved, the necessities and possibilities of applying reactivation processes to the catalyst, etc. Various modiflcations such as introducing diluents, refrigerants, heat carriers, reactants, and the like, multipoint along with or separately from the multipointinjected catalyst, may be used as found advantageous for any particular process.

A numerical treatment may be used at this point in order to bring out more clearly the hereinbefore discussed principles upon which the invention is based. A number of assumptions will be made to eliminate variables and simplify the presentation. A simple example would be an endothermic conversion involving heterogeneous catalysis, for example the conversion of an organic fluid using a solid contact catalyst in nely divided form. The data below will show how the invention is utilized to maintain a constant reaction rate by overcoming the effects of decreasing temperature, decreasing concentration of reactants, and any deactivation of the catalyst, which would, if the invention were not used but the same total conversion were obtained, cause the reaction rate to drop to a value in the last part of 'the reaction zone equal to only one-sixth that at the first part of the reaction zone. Assume no change in volume of reactants upon reaction, and assume that doubling the number of particles of catalyst will cause twice as much reaction to occur in a given time due to the doubled area of catalytic contact surface offered the reactants. Let a cylindrical reaction zone through which reactants and catalyst flow concurrently at the same rate be considered as divided into six cylindrical increments of equal volume referred to hereinafter as unit volumes. Let 0.5 unit volume of reactants enter one end of the reaction zone per minute, and a total of 0.5 unit volume of catalyst enter the zone per minute in equal increments of 0.083 volume at eachof six equally spaced points; that is, 0.083 volume of catalyst is introduced into each of the six aforementioned incremental unit volumes of the catalyst zone- In the rst unit volume of the reaction zone, the ratio of volume of catalyst to volume of reactants is in the sixth and last unit volume of the reaction zone the ratio is 1.0 WVU times that at the inlet, and accordingly, the effect on the reaction rate would be to increase therate 11 times. Considering now the contact time. it will be seen on following 0.5 volume of reactants through the catalyst zone that it requires minutes to traverse the iirst unit volume of the zone and minute to traverse the last unit volume 0f the zone. Thus it is seen that the contact time of reactants with the particular amount of catalyst present in the various zones is less in the later increments of the reaction zone than in the earlier increments, and therefore the tendency is for the extent of conversion to decrease. The effect of contact time alone on extent of conversion is equal to that is, the conversion would be approximately halved. Taking the two effects of contact time and ratio of catalyst to reactants, the overall tendency toward change in conversion could be approximately expressed as These figures indicate quantitatively the tend-y ency toward increased reaction rate caused by the multipoint introduction of catalyst in"` the exact manner just described, which tendency may be used to maintain a substantially constant overall reaction rate by counteracting the effects of suchv changes in reaction conditions as drop in temperature due to the endothermal nature of the reaction and/or decrease in concentration of reactants, etc., to the extent that any of such changes in conditions, or the effect of all combined, tend to cause a six-fold decrease in reaction rate. In similar cases in which the depressing inluences on the reaction rate are greater or less than six fold, the rate would be held constant by a corresponding increased or decreased overall ratio of catalyst to reactants, or by a controlled change in the activity of catalyst introduced at succeeding points, etc.. the exact conditions being calculated in a manner similar to that shown above. Application of this type of procedure to a specic endothermal reaction will be described in more detail hereinbelow with reference to Figure l. In order to explain the invention more fully, the following examples and appended drawings areprovided to illustrate specic embodiments of the process, but no limitations are thereby implied, inasmuch as the invention may be utilized in numerous other manners by following the teachings of this disclosure.

Figure l shows in diagrammatic form an ar rangement of equipment for carrying out the catalytic cracking of petroleum oils, an endothermic reaction, using a nely divided solid catalyst suspended in vaporous reactants and thus iiowing concurrently therewith, commonly termed a liuid catalyst process.

Figure 2 shows diagrammatically apparatus for polymerizing butenes, an exothermic reaction, in which a gaseous catalyst immiscible with the liquid reaction mixture is passed countercurrently to the reactants.

Figure 3 is a diagrammatic drawing of apparatus used for the vapor phase reduction of nitrobenzene with gaseous hydrogen, an exotherrnic reaction, wherein a metal catalyst supported on a solid granular carrier material is passed concurrently with, but at a different rate than, the reactants.

Figure 4 is a self-explanatory diagrammatic drawing ofv apparatus wherein a solid mobile catalyst is passed countercurrently to a uid reaction mixture, as in the case of the exothermic polymerization of olens with an increasing temperature gradient in the direction of flow of reactants as described hereinbelow.

-In Figure 1. the reactant, for example gas-oil derived by straight-run distillation of crude petroleum, passes from line lll into blower ii, and thence through line l2 into heater i3 wherein it is raised to a suitable temperature such as 900 F. for the initiation of the reaction upon contact with the catalyst. From heater i3 the heated reactants are sent through line I4 into the reaction chamber I5. This reaction chambermay take the form of an elongated tube, as shown diagrammatically in Figure l. Various types of reaction chambers suitable for use with powdered catalysts are known in the art. A very nely divided solid catalyst is injected into reaction chamber l5 at spaced pointsY along the path of flow of reactants through lines I6, ii, I8, and I3. Obviously, although only four lines are shown, the number of such lines may be varied at will to obtain suitable operating conditions compatible with economy of equipment. The catalyst may be of the natural clay type such as fullers earth, bentonite, etc., preferably activated in known manner, or of the synthetic type such as silica-alumina or other effective catalysts known to the art. The method of introducing the nely divided catalyst into the reaction zone may include such operations as suspension in liquid or gaseous reactants or diluents.

The catalyst may enter lines I6, Il, IS, and i9 from two sources. The rst source is conduit which carries recycled catalyst which has been partially deactivated by previous use in the process. The second source is conduit 2l which carries regenerated catalyst from catalyst regeneration zone 22. Carbonaceous deposits are removed from the catalyst in zone 22 by burning in an oxygen-containing gas. The quantity of catalyst from each source injected at each point is regulated by suitable means so that all of the catalyst entering through line I6 is the partly deactivated catalyst from conduit 20; most of that entering through line l1 is of the same type, but has admixed with it by means of line 23 a small portion of freshly regenerated catalyst from conduit 2|; that entering through line I8 vhas a larger proportion of reactivated catalyst,

which reaches line I8 through line 2li; and that entering at the last point through line i9 is composed entirely of renegerated catalyst from conduit 2|.

The mixture of products, excess reactants if any, and catalyst passes from reaction zone l5 through conduit 25 into a catalyst separation zone 26, which may be a cyclone separator, electrical precipitator, or any other suitable means for accomplishing the separation of nely divided catalyst from the hot vapors. Catalyst passes from zone 26 into conduit 21and a portion is taken from conduit 2l through conduit 28 to the catalyst regeneration zone 22. Vapors leave the catalyst separating zone 26 through line 29, and may be condensed and fractionated to separate out the desired cracked gasoline product, with unreacted gas-oil being recycled to the reaction chamber. If desired, various other modications of such a cracking process which are known to the art. for example recycle of veriy small amounts Aof hydrogen, etc., may be used.

The cracking of petroleum oils is an endothermic process, and, as heretofore explained, under ordinary methods of operation a substantial temperature drop occurs which causes a decrease in reaction rate as the reactants proceed through the cracking zone. However, by controlling the relative volumes of partially deactivated and of activated catalyst and also the total volumes of the catalyst introduced into the reactionzone as just described, in conformity' with the principles heretofore discussed in detail, the total catalytic activity at each succeeding point in the cracking zone in the direction of flow of reactants greater than the activity at the preceding points, the increase in activity being such that the normal decrease in reaction rate accompanying dropping temperatures and catalyst deactivation is partially or cornpletely obviated. This increase in total catalyst activity is obtained by the increasing volume of catalyst due to its multipoint introduction, and the increasing activity of the catalyst introduced, dueto the use of relatively greater proportions of freshly reactivated catalyst in the increments introduced along the path of flow of reactants. Of course, the actual quantities of catalyst introduced at the various points will depend upon the catalyst being used, its rate of deactivation under the given reaction conditions, rate of flow of reactants and catalyst, extent of reactivation effected in the catalyst regeneration zone, the characteristics of the gas-oil being cracked, temperature and pressure conditions'in the cracking zone, extent of indirect heat exchangeoccurring between the cracking furnace and any outside sources of heat or cooler surroundings, etc. However, the general principles set out in this disclosure will readily enable one skilled in the art to correlate these various factors for any particular application to obtain the advantages of the invention. Although in the drawing the rst point of catalyst introductionv into the reaction zone is shown past the reactant inlet, this rstpoint may also be positioned at or just before the inlet so that the first increment of catalyst enters along with the reactants.

It will be noted that in the cracking process as shown in Figure 1, several of the aspects of my invention which were described before in some detail may be involved. For example, the endothermic nature of the reaction will, unless sufficient heat exchange is provided, cause the temperature to drop. The multi-point introduction of catalyst is so controlled as to counterbalance this eiect in order to maintain desired reaction velocities. The catalyst during its travel through the cracking zone becomes at least partially deactivated, thus tending to slow the reaction even at constant temperatures. Additional catalyst, including regenerated catalysty is introduced in such quantities as to compensate for the deactivation occurring in the cracking zone. Another factor tending to decrease reaction rates is the decrease in concentration ci reactants which occurs as the reaction proceeds. Since in a gas-oil cracking process of the type described, only partial conversion, say from 15 13 to 40 per cent, is permitted to occur in one pass. the decrease in reactant concentration does not influence the course of reaction so much as in the' Acase of reactions giving complete conver sion-in a single pass. However, any effect oi this kind is readily overcome by the controlled addition of catalyst at the different points along although this is diiicult to accomplish in actual practice, at least by direct means. In such a casek'catalyst addition at points would be controlledv to make up for the combined eiiects of loss in catalyst activity and change in reactant concentration. On the other hand, reaction conditions may be maintained which are so mild that the amount of catalyst deactivation occurring in asingle pass will be very slight, so that ,the principal purpose of introducing the catalyst at points will be to compensate for decreasing temperatures and/or concentration or reactants in order to maintain a substantially constant reaction rate.

In Figure 2, an elongated reaction chamber 4B is provided, the interior of which may be filled with packing material for promoting intimate contact between gases and liquids. Fed to the system through line 4| is a gaseous hydrocarbon mixture containing ra substantial proportion of butenes, preferably isobutylene al though normal butenes may also be present. This gas is compressed in compressor t2 and then passes via line`43 to heat exchanger lit where it is cooled by indirect exchange with eiiiuents from the `reaction chamber. From the heat exchanger the cooled hydrocarbons pass via line 45 into the top of reaction chamber 40, wherein they are subjected to the polymericu ing. action of boron triluoride (BFS) as hereinafter described. Refrigeration means lit is interposed inline t5, and serves to cool the reactant feed-to the desired reaction temperature, in this case +30 C. rhe hydrocarbons making up the feed-,are in .liquid phase at this temperature, and the 'reaction chamber is operated at substantially atmospheric pressure.

Ordinarily a C4 fraction is used which contains substantial amounts of butanes, which serve as adiluent and as a solvent for the high molecular Weight polymers formed in the reac tion. If such butanes are not available admixed with the butenes, they may be supplied, or per tane or other suitable saturated hydrocarbon solvent may be used. The liquid butenes and accompanying hydrocarbons flow downwardly in chamber d countercurrent to gaseous BFs' and gaseous propane, and substantially complete polymerization of the butenes occurs to form polymers of a molecular weight suitable for use as lubricating oils, additives to oils, etc.

-The boron fluoride catalyst passes from con-l duit 41 into reaction chamber i6 at a plurality of points by means of valved lines den-48'@ inclusive. Also introduced into chamber 4B at thefsame points is liquefied propane from conduit 49 via valved lines SDA-50G inclusive. This li'quid'propane acts as a coolant, diluent, and disperant for the BFa, as-will be explained in more detail below. Ordinarilyv a catalyst acti# vator such as hydrogen fluoride, or other materials which will cause the production of hydrogen halides in the reaction zone, is introduced in small amount along with the boron iiuoride or otherwise. Furthermore, vmetallic nickel or other metals are occasionally used in the reacf tion zone to help catalyze or promote the reaction.

The butenes upon rst entering chamber :llt and beginning their downward new therethrough come into contact with a gas phase which coinprises propane and BFa. The volume o the gas phase is 'greater at this point than at any other point in the chamber. Polymerization is initiated by the catalytic action of the. boron iluoride. Thisfpolymerization reaction is highly exothermic, Aand the temperature must be held under very careful control, particularly since the type of product obtained may change greatly with a relatively small change in temperature; that is, the product formed at @30 C. may have an average molecular weight several times that oithe product formed at 0 C. For this reason, it is preferred to carry out the reaction as nearly isothermally as possible.

The amount of boron fluoride introduced will ordinarily vary from point to point, being i smallest at the top point .(conduit 48A) and greatest at the bottom point (conduit 48(5). By this multipoint addition of the catalyst, a much more eiicient reaction control is realized, since the reactants do not contact the total amount of catalyst at once. The catalyst contacted at the iirst point `comprises not only that introduced through conduit 48A, but also any bubbling up from the lower part of the reaction chamber. Just enough is introduced through line 48A to furnish sufficient fresh catalyst to initiate the reaction to the desired extent. It will be seen that the downward-owng reaction mixture continuously contacts upwardly flowing catalyst. Due to the formation of complexes between boron iuoride and olens, a substantial part of the catalyst combines with reactants and is carried down as complex. Such complexes have only a limited amount of catalystic activity, if at all. Thus, if all the catalyst were introduced at the bottom, it would be continuously reacting with olens as it rose through the chamber, and the upper part of the chamber would be decient in catalyst. In order to ensure that some catalyst reaches the top of the chamber, an otherwise un-` necessary excess would have to be introduced at the bottom.' Much better results are obtained by the multipoint addition, by which each increment added to the gas phase flowing upward through the reaction chamber can be controlled in amount to give just the desired concentration of catalyst at the given point. It is preferable that the amount of catalyst be relatively small at the top of the chamber where the reaction starts, since the major part of the reaction and thus heat evolution generally occurs in the upper half of the chamber where the greatest concentration of monomers is found.

The introduction of controlled amounts of cold liquid propane at 'points along with'the catalyst gives effective control of tf-:niper'aturel throughout chamber 4D. The propane vaporizes immediately upon entering the chamber, and in so doing absorbs the heat of reaction. Of course, additional indirect heat exchange may be provided for chamber 60 to assist in removing the heat of reaction if desired, particularly-in order to i avoid having too large an amount of -gaseous propane passing through the reactor.-y A convenient way to do this is to pass chilled liquid propane through coils in chamber 4U in indirect heat exchange with the reactants, and then to pass the desired amount ofthe propane into conduit 49Yfor direct introduction through conduitsSA, 50B, etc.v

Since the amount of BFs used in only a small percentage of the hydrocarbons charged, say from 0.5 to 5.0 mol per cent, the propane gas is very effective in promoting a morethorough disposal of the catalyst throughout the reaction zone. 'It also serves as a diluent both for the liquid reactants and for the gaseous vBFs.-V For this reason, larger amountsoi' BFa may be passed through reaction chamber 40 thus admixed with propane than would be suitable in the absence of the added gas. This excess BFsis recovered and recycled. The amount of liquid propane added through the lower conduits, for example, G to 50E. is less than that added through the upper conduits such'as 50A and 55B. This is because more heat of reaction is developed at the top of chamber 40 than at the bottom, and more evaporation of propane is needed'at the top to maintain the desired low temperature. y

'Flow rate of reactants through chamber 49 is preferably such that substantially no unpolymer-ized butenesare present in the efuents and thepolymers .in the effluents are predominately of high molecular weight, for example over-2000. The character of the polymers can be controlled to a certain extent bycontrolling the reaction time and thus'the extent of conversion, although f a change in operating` temperature `will generally have more influence on the final product. A short conversion time will ordinarily produce some of the high molecular weight polymers, with a larger' percentage of intermediate polymers which may be used for different purposes or which may be recycled to reaction chamber 40. The volume of propane gas passed through reaction chamber 40 will generally be several times the volume of liquidreactants and solvent passed through the chamber-n a given time. Y

Propane gas and boron fluoride gas leaving the top of chamber 4E) via line 5| are compressed in compressor 52, chilled, by-partial evaporation in known manner, if desired, in refrigeration means 53 to condense liquid propane, and then passed to accumulator 54. Cold gaseous boron fluoride leaves the top of accumulator 54 through line 41 for re-use in the process, while cold liquid propane leaves the bottom of accumulator 511 by line 49 to be-introduced into chamber 40 as described above. Of course, the gas phase from accumulator 54 contains some propane, and the liquid phase contains some boron fluoride in solution.

Since butenes are appreciably volatile at the temperature of operation of chamber 40, the gas leaving that chamber via line 5| has some butenes in it', and these butenes tend to undergo some polymerization in line 5| and compressor 52. For this reason, it is desirable that the length of line 5| between'chamber 50 and compressor 52 be short, and that the line 5| and compressor be flushed periodically with a solvent for the. polymers such as liquid butane. Not much trouble is experienced from compressor 52 on, since liquid propane is present which acts as solvent. The amount of -polymer small compared to the amount of butenespassinert-111s :cartonne- Sytem.; most of :the butenes formed is i6 returning unchanged intofreaction chamberU along with the propane.` A very satisfactoryway to obviate any dimculty in this regard'f-is tdwash the gas in line 5i with sufficient liquid butaney or pentane to remove practically all of the butene. The liquid may then flow directly into chamber 46. rihis modification is not shown in the draw? ing for the salte of simplicity.

Liquid products leave the bottom of reaction chamber 45 through line-55 and pass through heat exchanger 44 to be warmedto a higher. temperature and to cool the incomingfbutenes.,A From exchanger 44 the products pass vialine 56 .to separator 5l wherein dissolved and/ or. entrained boron iiuoride and propane gas are evolved, which pass via line 58 to line 5| for recovery; and

through line 6 turned to the system by lines 6 2, 58, and 5|.y O rdinarily heating the product to C. or higher will serve to release at leastpartof theboron.

iiuoride from the hydrocarbons.v Polymerisremoved from the system at 63. BF.; and/or propane required maybesupplled through line 54.

The above-described process exemplifies an adaptation of my invention to a highly exothermic reaction wherein the temperature` isqmaintained constant. The multipoint addition, of catalyst is controlled with respect to two principal variables. One is the loss of catalyst by com plex formation. Catalyst is added atpointsto maintain the desired amount of active catalyst.

The other is change in concentrationof-reactants. The smallest concentration of catalystis maintained at the point of greatestconcentrationl of butenes, while the greatest concentration of V,- catalyst is at the outlet where reaction is being completed with practically no butenes remaining.

It is to be noted that due to the diluent effectofy the gaseous propane, the actual quantity of catalyst may under certain conditions be greater at the top point than at the bottom point, but theratio of catalyst activity to reactants decreases] from bottom to top, the diluted catalyst vhavingless effect than the undiluted catalyst. Thecat alyst activity thus changes in relation to the extent of reaction, to compensate at least in part point is so controlled and correlatedvwitlr-thev other factors that catalyst activity at the Apointof greatest tendency toward heat evolution, thatl is the butene inlet, is smaller than at any other point, and the catalyst activity is increased as the tendency toward heat evolution decreases. The entire process may be contrasted with the prior art methods wherein theboron fluoride is added all at one point with consequent violent reaction at that point with little or no reaction at other points or wherein inefcient batch methods ,are employed with vigorous stirring,- gradual addition of catalyst and/or reactants is resqrlitdV Any malte-up.4

17 to, and the reaction time is unduly extended because of the inherent limitations of that method of operating.

Other specific applications of the principles of this invention to polymerization reactions are described in detail later on in this application.

In Figure 3, the reaction chamber 'l0 is preferably provided with means (not shown) for removing at least most of the heat of reaction by indirect heat exchange. A certain amount of heat is also lost to the atmosphere, but in order to avoid uneven cooling the entire chamber is ordinarily provided with some insulation. Heated vaporized nitrobenzene from line 1I and hydrogen from line 'l2 join in line '13, and ow into reaction chamber for downward flow therethrough. The hydrogen may be admixed with substantial amounts of carbon monoxide, or with inert gases such as methane or nitrogen.

In fact, vin carrying out the reduction of nitrobenzene in accordance with the present invention, I prefer to have some inert gas with the hydrogen. The ratio of hydrogen to nitrobenzene must be held within relatively narrow limits to obtain the highest yield of aniline, since a ratio considerably higher or lower than the stoichiometrical amount gives rise to reduction products other than aniline. It is best to have somewhat `more than the theoretical ratio of hydrogen to nitrobenzene, but not too much more, in order to ensure completion of the reaction, and some inert-gas is preferably used in admixture with the hydrogen.

A suitable supported hydrogenation catalyst in granular form is caused to pass through conduit 14 into manifold 15. y Branching off from manifold 15 are branches 16A-16F inclusive through which the catalyst is introduced into the reaction chamber 'IIJ at spaced points along the path of ow of reactants. The quantity of catalyst introduced through each branch 16A, etc., may be controlled by vany suitable means. It will be appreciated that due consideration must be given to the fact that chamber 'IIJ is operated under pressure. The lines, 16A to TEF inclusive, are shown equally spaced; however, the lines may be more or less in number, and evenly or unevenly spaced, in accordance with the capacity of the system, convenience of fabrication, operating conditions, rate of catalyst introduction at the various points, and economy of equipment. A series of bailes 'Il is provided in chamber 'l0 to keep the catalyst particles dispersed and in good contact with reactants as the catalyst falls to the 4bottom of chamber 10. These baffles preferably Yhave only a slight inclination from the horizontal so that catalyst is more or less pushed off of one bafe down to the next by incoming catalyst.

In the hydrogenation of nitrobenzene by prior methods, the reaction mixture is passed through a stationary bed of catalyst. Since the concentration of reactants is greatest in the first portions ofthe catalyst bed, the major part of the reaction occurs before the bed is halfway traversed. This means that the amount of heat liberated in the upper parts of the catalyst chamber is greater than in the lower parts, and thus the load on heat exchange coils or the like with which the chamber may be provided is greatest at the top and least at the-bottom. Thus the heat exchange means must either be oversized at points or is overloaded. `In` practical operation, the heat of reaction cannot be satisfactorily removed, and a serious temperature rise occurs. This is very undesirable, since the optimum yield of aniline,

when using any given catalyst, is obtained only in a relatively narrow temperature range. Sintering of catalyst is also likely to occur on the most active catalytic points Where the actual temperature may be from 25 or 50 to a hundred or so degrees centigrade higher than the mean temperature of the reactants and catalyst near those points. A further disadvantage lies in the fact that the temperature riseserves to increase the already excessive reaction rate still more.

By means of my invention the catalyst addition is controlled in accordance with the rate of reaction or rate of evolution of heat, so that substantially equal, or at least regularly varying quantities of heat are evolved and removed along equal increments of the length of reaction chamber T0. Thus, in the first part of reaction chamber l0, a relatively small amount of catalyst is introduced through branch 16A. Since the highest concentrations of nitrobenzene and of hydrogen are found in this portion of the reaction zone a small amount of catalyst is suicient to promote considerable reaction. As the reaction rate tends to lessen due to the diluent eiects of the aniline formed, or stated another Way, due to the lowered concentrations of nitrobenzene and hydrogen, additional catalyst enters the reaction zone through 16B, and the reaction rate tends to increase again. Thus, the quantity of active catalyst surface present at various points in reaction chamber l0 is maintained suiciently, as the reactants flow therethrough, so as to give a completely reduced product in the ellluents. The amount of catalyst in the parts of chamber 'I0 is small at the inlet thereof, and increases gradually toward the outlet, where it reaches a maximum. The reaction rate is maintained more or less constant throughout the reaction zone, in contrast to other methods wherein the last half of the catalyst chamber may be used for effecting only ve or ten per cent of the total conversion. The temperature may be maintained substantially constant due to thefact that the amount of heat liberated is not excessive at any point, or a gradual temperature gradient may be allowed to exist, an increase of say C. from the inlet to the outlet being permissible without undesirable effects. It is to be noted however, that in using my invention, such a temperature gradient is regular, and is obtained gradually as the reactants flow through the apparatus, rather than being obtained all at once as by other methods, in which case a peak temperature may even occur, with a subsequent falling off in the latter stages where very little reaction is occurring.

A certain amount of catalystdeactivation will occur which tends to lessen the reaction rate, and this is also compensated for by the fresh catalyst added. The rate of `catalyst deactivation will of course depend upon the catalyst used, the severity of reaction conditions, and particularly upon the purity of the reactants. Generally, the amount of catalyst poisons present in the nitrobenzene and hydrogen gas is small, and catalyst deactivation is not of great consequence in lessening the reaction rate in the passage of catalyst from vtreatment to which the catalyst is sub'fected outside the chamber. .It is usually preferable to reactivate the catalyst before it has lost too much of its activity, since considerably higher temperatures frequently must be used in the reaction zone with a less active catalyst. Thus it is seen that a continuous iiow of catalyst is maintained through chamber 'l0 so that the catalyst as removed from the bottom thereof is usually still fairly active. The rate of ow of gaseous reactants through the catalyst chamber 'l0 will be many times greater, on avolume basis, than the rate of flow of catalyst therethrough.

The total effluent from reaction chamber 18 passes out through conduit 'i8 and then to catalyst separatorl 18 where the catalyst separates from the gases by gravity. This catalyst is removed through conduit 88 containing suitable .conveying means such as screw 8 l. From 88 the catalyst passes through conduit 82 to conduit 14 for re-use in the process. lyst stream may be continuously by-passed through a'regeneration zone indicated diagrammatically at 831 to maintain thertotal catalyst stream at the desired activity. The regeneration in Zone 83 comprises conventional chemical treatments to remove accumulated impurities and to restore the catalyst to substantially its original conditions. The entire stream of catalyst. rather than a portion, may be passed through regeneration zone 83 if desired.

The gases in catalyst separator 'i9 comprise aniline produced in the process, any traces of undreduced nitrobenzene, steam formed as a byproduct, any excess hydrogen, and any inert gas introduced along with the hydrogen. This gas phase is passed via line 84 through cooler 85 and into product separator 8S, wherein a liquid waterrich phase, a liquid aniline-rich phase, and a gaseous phase separate out. The gas is recycled via line 81 to line 12 for re-.use of the hydrogen in the process. In order to prevent inert gases from pyramiding in the system, a portion of the gas is allowed to leave line 81 through valved branch 88. The aniline is removed from separator 86 through line 89 and passed to suitable apparatus for removing dissolved water and any other impurities. Water is removed from separator 86 through line 98, and passed to a system for recovering dissolved aniline therefrom. One very effective method of accomplishing this is to extract the aniline from the water with nitrobenzene, the extract then being led to the reaction zone for reduction of the nitrobenzene.

Suitable catalysts for the reduction of nitrobenzene according to the system just described may comprise metals such as gold, silver, nickel, copper, or tin, either alone or in admixture, and preferably supported on granular carriers such as pumice, porcelain, alumina, etc. It is necessary that the catalyst composition have sufficient mechanical strength for withstanding the effects of continuously moving through the equipment. A preferred catalyst comprises supported tin prepared from the precipitated hydroxide or carbonate. With such a catalyst, an operating temperature in reaction chamber 70 in the range of about 275 C. to 375 C. is suitable.

The processes described above with reference to Figures 2 and 3 have illustrated two specio methods of eifecting cxothermic reactions, viz., polymerization and hydrogenation, respectively. It will be appreciated that some of the principles of the invention and procedures described herein will be applicable to exothermic reactions as a class, with suitable modifications being made in A portion of the catalpossibly more types.

view of Vparticular .known characteristics of 'specie reactions which may vdiffer from one reaction to another. Thus, polymerization reactions broadly are comprehended within the Scope of this disclosure. .Polymerization may be broadly considered to be any chemical combination of two or'more similar molecules to form `a single molecule, the reaction usually involving primary valence'forces. The combining-molecules may be all of the same kind, or they may be of two and The most Common and largest number of polymerization vreactions involve organic molecules which ycontain an vunsaturated carbon-to-carbon linkage, for example, a double bond. Polymerization in the presence of a gaseous, liquid, or solid catalyst may be carried out with the reactants in the vapor or liquid phase, at high or low temperatures and at high or low pressures. TheY loperating conditions are known and will varyaccording to the reactants, the catalyst, and the type of products involved.

Y Many types of polymerization are known, for example, the reactions involving vinyl compounds such as styrene and vinyl chloride, unsaturated acids, ketones, nitriles, and the like, 'olens dioleflns, acetylenes, and condensation reactions of aldehydes, urea plus formaldehyde. etc.

One preferred modification comprehends the polymerization of low-boiling olefins at elevated temperatures to form liquid fuels. A suitable arrangement of apparatus is shown diagrammatically in Figure 4, including provisions for blending regenerated and unregenerated ycatalyst if desired. For example, Va mixture of three and four carbon atom hydrocarbons containing propylene and one or more butenes, and preferably containing considerable quantities of isobutylene, is passed upwardly in the vapor phase, or in the liquid phase, through an elongated reaction zone countercurrent to a downwardly owing stream of granular synthetic silica-alumina type polymerization catalyst. Such catalysts are made from hydrous silica gels activated vwith minor amounts of alumina or zirconia or other metal oxides and are well known in the art; hence detailed discussion of their composition is not necessary at this point to a full understanding of the invention. This type of polymerization will take place in the presence of an active catalyst at temperatures of about 250 F. However, the reaction is not particularly sensitive to temperature, and satisfactory products may be obtained at temperatures within the range of say 250 to 400 F. or even somewhat higher. The reaction is ofcourse highly exothermic and due to the lack of sensitivity to temperature just mentioned the temperature may be allowed to rise substantially in the direction of iiow of reactants through the reaction zone without adversely affecting the final products. While some heat exchange may be employed in order to minimize the temperature rise it is not necessary to remove all the heat of reaction when operating in accordance with the present procedure. This desirable result is obtained by introducing the granular catalyst into the reaction zone at a plurality of points along the length thereof, the quantity and activity being controlled in accordance with the principles herein before outlined so that as the reaction mixture proceeds upwardly in the reaction zone the activity of catalyst encountered is substantially constantly decreasing; in this connection by activityl mean the total catalyst activity available, as affected by quantity and/or activity of a given portion of catalyst.

` lThe catalyst may be introduced by known means and allowed to move slowly down through the reactor, for example in a reactor constructed similar to that shown in Figure 3 which includes baiies for slowing the flow of catalyst. The apparatus of Figure 4 can be so constructed. In this modification the reactor is not maintained full of catalyst but rather the catalyst is allowed to move slowly down from one bafe to another. Thus, the reaction mixture when first introduced contacts a maximum of catalyst at a minimum inlet temperature. The inlet temperature is chosen with respect to the particular catalyst and reactants so that in the presence of the particular quantity of catalyst present in the lower part of the reaction zone the reaction will be initiated. As the reaction proceeded upwardly, the temperature tends to increase duc to the exothermic nature of the reaction. This increase in temperature causes an increase in re.- action rate which would soon cause the reaction to run away if the same amount of catalyst were being contacted. However, in the practice of this invention the amount of catalyst in the reaction zone constantly decreases in the direction of flow of reactants and this decrease in catalyst tends to off-set the eect, on the reaction rate or extent of reaction, of the increasing temperature just mentioned. While the decrease in concentration of reactants in the direction of iiowof reactants tends to cause a decrease in reaction rate, the heat liberated is sufficient that the temperature can be allowed to increase to such extent that the effect of temperature on the reaction rate will more than overcome the effect of decrease in concentration of reactants. By contacting less and less catalyst as the reaction mixture nears the top of the reactor the overbalancing effect of temperature is compensated for. As an example, the inlet temperature may be '250 F. and the outlet temperature at the top may range from 350 to 400 F. with catalyst of the usual activity.

If the reactor is maintained substantially full of catalyst so that it moves downwardly therethrough as a moving bed thus dispensing with the use of baiiies, the activity of catalyst introduced at the various points must be controlled so that the activity in the upper portions of the moving catalyst bed is less than the activity in the lower portions. This can be done by partial regeneration of the catalyst and blending of reactivated and unreactivated catalyst in varying portions as described hereinbefore. See Figure 4. In any manner of operating, part or all of the unreactivated or reactivated catalyst may be introduced into the reaction zone at a temperature esters.

22 acted to form hydrocarbons suitable 'for use as fuels. By control of ratios of reactants, temperatures, contact times, and catalysts, the products may range from gases to solid waxes, and

from essentially hydrocarbons to essentially oxygenated hydrocarbon derivatives. The particular process of this type of commercial interest at the present time involves the reaction of a synthesis gas containing about two mois of Hz to one mol of CO, in the presence of a cobalt or iron catalyst, to form gasoline-boiling-range hydrocarbons, along with substantial amounts of oxygen containing aliphatic compounds includ;- ing alcohols, aldehydes, ketones, acids, and The reaction is believed to involve a preliminary formation of methylene, i. e., -CH2-, groups, several of which unite or polymerize to form at least some of the reaction products, and hence may be broadly thought of as involving polymerization as well as other reactions. However, the over-all conversion has` characteristics distinguishing it from other conversions. Ordinarily the temperature must be controlled within very narrow limits to produce a given product, and since the reaction is highly exothermic this involves the removal of large quantities of heat from the reaction zone. In some instances, however, a limited temperature rise may be permitted. Application of various principles of the present invention as set forth hereinabove will be apparent on consideration of the specic attributes and requirements ofthe Fischer-Tropsch type synthesis.

For example, the procedure just described in which olens are polymerized in the vapor phase in the presence of a granular catalyst moving counter-currently to the reactants, the temperature being allowed to rise appreciably in the direction of iiow of reactants, may beY used for the synthesis reaction provided the temperature rise is limited, by removal or absorption of some heat of reaction, to a smaller gure than that allowable in the polymerization of olens. Thus, with a sintered iron catalyst, a H2:CO ratio-of 2: 1, and a reaction temperature in the neighborhood of 600 F., the inlet temperature may be 575 F. and the outlet temperature 630 F., only sufficient heat being removed by heat exchange coils or tubes in or around the reactor or by other known methods to establish a regular and deliberate temperature rise; the catalyst in pellet or even powdered form is passed into the vertical reactor at a plurality of points and passed downwardly through the reactor, removed from the bottom, and returned, with or without reactivation, to the inlet points again. The higher the considerably lower than the reaction temperagreatly limited by use of indirect heat exchange or otherwise, but the heat exchange require- Y,

ments in the various sections of the reaction zone being equalized by virtue of the controlled introduction of catalystas described.

Another conversion process in which the principlesof the invention are applicable is that comf monly known as the Fischer-Tropsch synthesis, in which hydrogen and carbon monoxide are re- 'f temperature the less catalyst contacted by reactants, with consequent advantages and results as described hereinabove.

If desired, the procedure of Figure 3 may be used for carrying out the Fischer-Tropsch synthesis, whereby temperature is held constant by removal of heat, catalyst and reactants flow concurrently, and the increasing amounts of catalyst encountered along the line of ow overcome the effect of the decreasing concentration of reactants. Likewise, heat removal and temperature control, are made easier as described by providing a more nearly equal extent of reaction throughout the various sections of the reactor.

The use of powdered sintered iron catalyst has proved to be of great advantage in this reaction, and this catalyst may be suspended in an upowing gaseous reaction mixture, the suspension being passed through vertical heat exchange tubes or contacted with other ,heat exchange means for removal of the heat of the Fischer-Tropsch reaction. Additional catalyst is introduced at a plurality of points along the length of the reactor, and an advantageous method of constructing the reactor isi-to superimpose a, series of vertical tube bundles, a space being provided between each two bundles by means of horizontal tube sheets intowhich space'catalyst is injected; the space also serves to ensure re-mixing of reaction mixture and catalyst at severalv points along the line of iiow. 'With or without the use of such heat exchange tubes, the velocity of gas flow may be sufliciently low to provide a so-called hindered settling of catalyst, by which all catalyst is eventually carried upward and out, but the average rate of flow of catalyst is less than the rate of flow' of gases, thus increasing the density of the .catalystsuspension kThis is particularly desiravble 'when the catalyst, as in this case, is only slowly deactivated.

In any of the foregoing methods of carrying out the synthesis of organic compounds from hydrogen and carbon oxides, the activity of catalyst introduced at each pointvmay be separately controlled by any suitable means, including the proportioning of unreactivated and reactivated catalyst. Specifically, the procedure of Figure 1 above may be utilized in any of the concurrent ilow vmethods in order to provide increasing activity each particular material treated. By following tions described, but only by the appended claims.

I claim:

1. The improved method of effecting catalyzed exothermic organic conversions which comprises passing a fluid reaction mixture to be converted through a reaction zone at conditions effective to obtain said conversion and so chosen that the temperature is caused to increase in the direction of flow of the reaction mixture due to the exothermic heat of reaction, introducing a solid mobile catalyst for the reaction into said reaction zone at a plurality of points spaced in the direction of flow, passing the thus-introduced catalyst through said reaction zone countercurrently to the reaction mixture, and separately controlling the quantity and activity of catalyst introduced at each said point to provide a decreasing amount of catalyst activity inthe direction of ow of reactants as an inverse function of the temperature thus tending to equalize the extent of reaction throughout said reaction Zone.

2. The process of claim 1 in which lsaid organic conversion comprises the polymerization of vat least one polymerizable organic material.

3. The process of claim 1 in Which low-boiling olens are polymerized in the gas phase in the presence of a synthetic silica-alumina type catalyst.

4. The process of claim 1 in which said organic conversion comprises thereaction of carbon monoxide with hydrogen to form aliphatic organic compounds, and in which a sufficient part of the heat of reaction is removed to limit the temperature rise to an amount avoiding undesired reactions.

THOMAS B. HUDSON.

REFEBENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,366,439 Weber Jan. 25, 1921 2,085,524 De Simo et al June 29, 1937 2,176,234 Wiezevich Oct. 17, v1939 2,347,682 Gunness May 2, 1944 2,370,816 Schonberg Mar. '6, 1945 2,378,651 Matuszak June 19, 1945 2,406,851 Redcay Sept. 3, 1946 2,429,161 Hudson Oct. 14, 1947 2,444,990 Hemminger July 13, 1948 

1. THE IMPROVED METHOD OF EFFECTING CATALYZED EXOTHERMIC ORGANIC CONVERSIONS WHICH COMPRISES PASSING A FLUID REACITON MIXTURE TO BE CONVERTED THROUGH A REACTION ZONE AT CONDITIONS EFFECTIVE TO OBTAIN SAID CONVERSION AND SO CHOSEN THAT THE TEMPERATURE IS CAUSED TO INCREASE IN THE DIRECTION OF FLOW OF THE REACTION MIXTURE DUE TO THE EXOTHERMIC HEAT OF REACTION, INTRODUCING A SOLID MOBILE CATALYST FOR THE REACTION INTO SAID REACTION ZONE AT A PLURALITY OF POINTS SPACED IN THE DIRECTION OF FLOW, PASSING THE THUS-INTRODUCED CATALYST THROUGH SAID REACTION ZONE COUNTERCURRENTLY TO THE REACTION MIXTURE, AND SEPARATELY CONTROLLING THE QUANTITY AND ACTIVITY OF CATALYST INTRODUCED AT EACH SAID POINT TO PROVIDE A DECREASING AMOUNT OF CATALYST ACTIVITY IN THE DIRECTION OF FLOW OF REACTANTS AS AN INVERSE FUNCTION OF THE TEMPERATURE THUS TENDING TO EQUALIZE THE EXTENT OF REACTION THROUGHOUT SAID REACTION ZONE. 